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WAS READY K)R A BIG-NO, MAKE THAT 5-/-G-SWAP.
ATK's new 605 Thumper and its revolutionary
single-sided frame had passed the extreme flex test. It is hard to comprehend
how a frame that connects the headset with only the lower-left swingarm pivot
could possibly be as rigid as an ordinary frame, but it is. And that's only the
beginning: Its design also allows a full 13.2 inches of rear-wheel travel, but
with a relatively low 36.5-inch seat height. Plus, it's 10 pounds lighter than
the conventional frame it replaces.
It is not at all strange for ATK to debut a revolutionary new concept on a motorcycle. Remember the company's A-trak chain-torque eliminator, from which the ATK name was derived? How about the countershaft-mounted disc brake? Those ideas worked on paper, but real-world conditions forced ATK back to more normal setups.
That should not be a problem with this new frame.
A completely redesigned stainless-steel exhaust pipe gets the gasses out with less restriction and flows through a large-core muffler capped off with SuperTrapp discs.
WP continues to produce suspension for ATK. The
40mm inverted fork has full adjustment, this year with compression in one leg
and rebound in the other. As per usual ATK practice, the side-mounted WP shock
is progressively valved and runs without a linkage.
The fuel tank is designed to call attention to
the new frame, and houses a claimed 3.6 gallons. The fenders and numberplate are
still sourced from Italian plastic maker UFO. Also on the thumbs-up list is the
new oversized front-brake rotor squeezed by a Brembo dual-piston caliper; much
improved over last year, though still a notch off Honda's class-leading stopper.
Though in the past Rotax motors have been finicky
about starting, the spot-on jetting of the ATK sorts this out. Warm-up is
quick-no coolant to heat here.
A wide powerband is one of the ATK's joys. Torque
is abundant, throttle response instant. It runs like a well-tuned Honda XR600,
but with a much smoother bottom-end power spread. The slow-revving nature of the
motor is deceiving, but ground speed tells the real story—the 605 simply ingests
off-road miles. There's really no need to rev the motor, but the fact that you
can shows its versatility.
Thumpers. Because the dual-purpose model makes up 95 percent of ATK big four-stroke sales, it comes as no surprise that the settings cater to fireroads more than supercross-style double-jumps. If your riding taxes the suspension, or the terrain gets nasty, the suspension has enough adjustment to handle the situation. During our visit to ATK's headquarters in Bountiful, Utah, I raced a kick-start version with stock suspension in a national hare & hound, and it worked admirably, rarely bottoming.
So, back to this half-a-frame concept. Riding the bike, you would never know that there is some weird, new-fangled frame beneath you. Made up of large diameter, thin-walled tubing, it resembles half a perimeter-style frame, but seems amazingly rigid. The wrapped-steel swingarm, just like the one on the two-stroke LQ model, is much stronger than the ol"d rectangular unit, and does its share to reduce flex, too.
The frame also carries the bulk of the engine's 3
quarts of oil. This feels great on a cold day, but the heat can get to a
sit-down rider's left thigh in warmer conditions. ATK has, however, taken
precautions: The fuel tank has threaded inserts to allow the mounting of a heat
There is plenty of room to move about on the ATK.
A long and spacious seat, and its relationship to the footpegs does not cramp
even tall riders. Ground clearance is not an issue, with 13 inches before a
frame rail touches down.
But it's small details that hurt the ATK: a
flimsy aluminum plate that supposedly protects the chain guide, but bends when
pebbles hit it; footpegs that are plenty strong and functional, but become dirt
scoops on contact with the ground; a flappy-flyer license-plate mount that
interferes with the tire. Sure, dirt riders love to tinker with their bikes, but
for this many dollars, they shouldn't have to.
Source Cycle World 1996